Make NeighborTrajectory simpler

[pmrv]

Pending #444.

[pmrv]

Thanks @sudarsan-surendralal I've been sloppy. :S

[coveralls]

Pull Request Test Coverage Report for Build 1526011310

• 16 of 22 (72.73%) changed or added relevant lines in 1 file are covered.
• 1075 unchanged lines in 30 files lost coverage.
• Overall coverage decreased (-0.02%) to 69.827%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pyiron_atomistics/atomistics/structure/neighbors.py	16	22	72.73%

Files with Coverage Reduction	New Missed Lines	%
pyiron_atomistics/atomistics/structure/factories/aimsgb.py	1	94.74%
pyiron_atomistics/atomistics/structure/phonopy.py	2	56.0%
pyiron_atomistics/atomistics/structure/analyse.py	3	98.48%
pyiron_atomistics/sphinx/potential.py	3	66.67%
pyiron_atomistics/atomistics/structure/factories/ase.py	4	90.91%
pyiron_atomistics/interactive/activation_relaxation_technique.py	4	95.56%
pyiron_atomistics/atomistics/generic/object_type.py	5	58.62%
pyiron_atomistics/atomistics/job/atomistic.py	6	72.77%
pyiron_atomistics/atomistics/structure/pyscal.py	6	87.1%
pyiron_atomistics/atomistics/structure/symmetry.py	6	93.14%

Totals
Change from base Build 1519855178:	-0.02%
Covered Lines:	11430
Relevant Lines:	16369

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💛 - Coveralls